Two-stroke cycle internal-combustion engine with slide valve



April 1952 J. T. M. SCHLAMANN TWO-STROKE CYCLE INTERNAL-COMBUSTION ENGINE WITH SLIDE VALVE 2 SHEETS-SHEET 1 Filed Jan. 24, 1949 FIG. I

HARD FACING META L LAYE R yohannes TM. Schmmann His A++0rney A ril 1, 1952 J. T. M. SCHLAMANN TWO-STROKE CYCLE INTERNAL-COMBUSTION ENGINE WITH SLIDE VALVE Filed Jan. 24, 1949 2 SHEETSSHEET 2 \nvenfor:

n h 0 mm m h C. 5 mW T Wm mm %A n n m H a Patented Apr. 1, 1952 TWO-STROKE CYCLE INTERNAL-COMBUS- TION ENGINE WITH SLIDE VALVE Johannes T. M. Schlamann, Delft, Netherlands, assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application January 24, 1949, Serial No. 72,516 In the Netherlands February 6, 1948 12 Claims.

This invention relates to two-stroke cycle, spark ignition internal combustion engines hav ing slide valves fitted to the piston to control the inlet and outlet ports in the cylinder wall for the admission of a charge and the discharge of combustion gases, respectively, the cylinder having a reentrant cylinder head extending downwardly into the cylinder. Engines of this general type are already known (vide British Patent No. 170,012) and are characterized by sustained high torque and high horsepower per cubic inch displacement, resulting from the high volumetric efficiencies.

Engines of this type have the advantage of low octane gasoline requirements. This advantage has heretofore not been fully realized. Another drawback of such engines has been the necessity of using iron or ferrous castings when the slide valve is cast integrally with the piston due to rapid wear when aluminum or aluminum alloy is used; this has been due to the difliculty in lubricating the slide valve. In consequence of the great mass forces resulting from the use of iron castings, the speed of operation of the engine was limited. In addition, the unsatisfactory heat-conduction properties of cast iron resulted in low heat transfer capacity and, hence, in low specific outputs.

The instant invention has for its primary object further improvement of engines of this type to reduce the tendency to knock due to detonation. For this purpose it is essential, inter alia, that no parts of the engine adjacent to the combustion space are kept hot and that residual gases originating from the preceding cycle should be removed as completely as possible. Accordingly, a specific object is to provide an engine of the type described having improved scavenging ar-' rangements, whereby such residual gases are removed more completely than was heretofore practicable, without counteracting the other measures taken to minimize detonation, such as flow of the gases to produce the correct type of turbulence and prevention of excessive temperatures.

A further object is to provide an engine of the type described wherein the piston and slide valve may be both made of light metal of good heat conducting properties, specifically, aluminum or an aluminum alloy, thereby achieving more favorable temperature conditions, and permitting the use of a lighter piston cast integrally with the slide valve. More particularly, it is an object to provide an engine with an aluminum or aluminum alloy slide valve having a part of the slide valve, viz., at least the face thereof on which the cylinder sealing rings are running, coated with a layer of a hard metal, such as chromium, whereby a sleeve is obtained which shows little wear and excellent heat transfer capacity, resulting in an engine having a high specific heat output.

Applicant has now found that by a correct combination of construction features, as will be defined hereinafter, very important improvements can be attained, whereby detonation can be greatly reduced or checked. It thereby becomes, possible either to use fuel of a lower octane number with the same or a higher compression ratio, or to increase the compression ratio with the; same type of fuel, which will result in better performance of the engine.

The engine according to the invention has the following construction: (a) The upper face of the piston and the lower (i. e., inner) face of the reentrant cylinder head or cap facing the piston are both slightly convex; (b) the part of the slide valve directly joining the piston face is thickened to such an extent that the combustion space remaining at the end of the compression stroke has a diameter of from about 0.75 to 0.85 of the internal diameter of the slide valve; (0) a plurality, preferably at least two and not over six, inlet ducts are formed in this thickened part of the slide valve, distributed uniformly about the periphery, and having an aggregate width (measured peripherally about the slide valve) of from about 0.4 to 0.6 of the circumference of the slide valve; and (d) the inlet ducts are directed to cause the projections of their center lines on a plane perpendicular to the center line of the engine cylinder to be tangent to a circle described in said plane about said center line of the cylinder and having a diameter less than the internal diameter of the thickened portion of the slide, preferably between about 0.1 and 0.3 of the internal diameter of the slide valve above the thickened portion, and these ducts are, further, directed with their inner ends higher, toward the vicinity of the upper edge of the thickened part of the slide valve. While certain of the advantages of the invention may be realized applying selected features, and the invention broadly contemplates the use of tangentially and upwardly directed inlet ducts in conjunction with an interiorly thickened slide valve, the full advantages can be realized only by utilizing all of the foregoing features in combination.

The engine cylinder will, of course, be provided with inlet ports Which will be intermittently in registry with the inlet ducts, and with exhaust ports controlled in any suitable way by the slide valve, preferably by means of exhaust ducts formed in the valve for intermittent registry with the exhaust ports, but permissibly by passage of the upper end of the valve away from the exhaust port.

While, in its broader aspects, the above-described engine may have a cast iron slide valve, which may be separate from or integral with the piston, it is more advantageous to employ a unitary piston and slide valve, cast integrally from aluminum or an aluminum alloy, and having at least the part thereof running in contact with the cylinder sealing rings coated with a hard metal, such as chromium. Not only does this result in a lower mass, permitting higher operating speed on that account, but the heat transfer characteristics are greatly improved thereby, resulting in reduced tendency toward detonating, i. e., a higher thermal load is made possible, through a higher compression ratio and/or a greater number of revolutions per minute.

The invention will be described more particularly in connection with the accompanying drawi'n'g' forming a part of this specification and illustrating one preferred embodiment thereof, wherein:

Fig. 1 is an eccentric vertical sectional view taken on line I'I at Fig. 4 at bottom dead center, and Fig. 2 is a similar view with the piston at top dead center; I

Figs. 3 and 4 are transverse sectional views taken on lines 33 and '44, respectively, of Fig. 1.

In this specification and claims, for conciseness, the end of the engine or cylinder axis toward the cylinder head is referred as the top, and the end toward the crankcase as the bottom, it being understood that the engine may be opera'ted in other positions.

The engine comprises a cylinder block having an inner wall I containing a piston 2 carrying a cylindrical slide valve 3-4 extending upwardly and downwardly from the piston face 5 and cast integrally with the piston. The slide valve, may be regarded as comprising two tubular skirts 3 and l. The cylinder is provided with a reent-r-ant cylinder head 6 carrying aspark plug 7, the latter being surrounded by a jacket tube 8. The head is spaced from the wall I to provide an annular recess accommodating the skirt 3, and the cooling space therein is closed by a cover 9 provided with flow passage I communicating with a cooling space -I I formed in the cylinder block between the inner cylinder wall I and an outer wall 12. Cooling liquid may be circulated through openings 13 and I4. The cylinder block is further provided with a plurality, e. g., four exhaust ports I communicating with the interior of the-cylinder having walls connecting the inner and outer cylinder walls as shown in Fig. 3, and located preferably near the bottom of the reentrant cylinder-head. Farther down the inner cylinder wall has a plurality, preferably two to seven inlet ports [6; these ports are located below the cooled porticn of the cylinder and communicate with the interiors of jackets I! for passage of the carburetted :gas or charge. The invention is not dependent upon any specific .mode of supplying the charge to the jackets Ill, and a separate compressor maybe used for this purpose; it is however, usually convenient to compress this charge within the crankcase. To this end the jackets communicate through a duct I8 with the crankcase .19, and an inlet port 20 is formed in the inner cylinder wall at a height to be uncovered by the skirt 4 of the slide valve when the piston is at the top as in Fig. 2. It will be understood that a charge of air and gasoline is supplied to the crankcase through port 20, and that this charge will be compressed within the crankcase when the piston descends. The depending skirt 4 extends down far enough to cover the inlet ports I6 at all times that the piston is making the upper part of its stroke; the skirt 3 may control the exhaust ports I5 in any manner, and in the illustrative embodiment shown it is suf- 'ficiently long to cover these ports at all times.

The piston carries piston rings 2I and 22 running against the cylinder wall I The main upper part of the skirt 3 of the slide valve has a thickness to fit into the annular recess between the reentrant head 6 and the cylinder wall I and has an internal seal with the former by means of stationary packing rings 23 fitted within annular grooves in the head. In order to prevent excessive wear of the inner face of the slide valve when made of aluminum or an aluminum alloy it is provided with a hard surface layer, e. g., 'a chromium layer. This layer can be applied electrolytically, by spraying, or in some other way to any desired thickness, e. g., 0.005 to 0.01 inch and ground to size, leaving a final coating of a few thousandths of an inch in thickness. If required, the outer surface of the slide valve may also be provided with such a hard-facin material.

Upper face 5 of the piston head and the lower face of the reentra-nt cylinder head 0 are both slightly convex toward one another. As is clearly shown in the drawings, the central crown of the piston face 5 rises above all parts of the lower margin thereof by a height which is less than the radius of the piston face.

The skirt 3 has a thickened part 24 close to the portion thereof joining the piston head, the thickness being sufiicient to have an internal diameter between about 0.75 and 0.85, e. g., approximately 0.8, of the internal diameter of the skirt 3 above the thickened part.

A plurality of inlet ducts 25 are formed in the thickened part 24, oriented for registry with and corresponding in number to the ports I6. These ducts may be circular in cross-section and are large enough to have an aggregate width (measured peripherally about the slide valve) of between about 031 to 0.6 of the inside circumference of the slide Ci. e. the main part above the thickened portion) ,e. g., about half of this circumference as shown in Fig. 4.

The ducts 25 are shown in horizontal projection in Fig. 4, from which it is evident that the center lines of .the ducts are not radial but that their projections on a horizontal plane are tangent to .a small circle of radius 1" which is equal to between about 01R and 0.3R, where R, is the internal radius of the slide, e. g., 027R as shown in the drawing. Further, .the center lines of these ducts are inclined upwardly toward their inner ends, as in Figs. .1 and 2, so that they are directed toward the upper edge of the thickened part 24. These ducts are located low enough so that their lower walls merge smoothly with the face 5 of the piston.

Further, the slide has outlet ducts 26 oriented for registry with and corresponding in number to the exhaust ports I5. As shown in Figs. 1 and 3, these rducts have their inner edges rounded in order to reduce the outflow resistance and thus to improve scavenging.

In operation, a. charge enters the crankcase through port 20 while the piston is at the top of its stroke, and compressed on the next downward stroke of the piston until the ducts 25 are in registry with the ports l6, permitting the compressed fresh charge to enter the space above the piston. The ducts 26 being at the same instant in registry with the ports l5, the fresh charge displaces the burnt gases, which escape through the ports I 5. When the piston again ascends the ports l5 and I6 are shut off by the slide valve and the charge is compressed; it is ignited by the spark plug 1 at any desired instant near the end of the compression stroke, and expands during the power stroke.

As a result of the specific features previously described important improvements are effected in the operation of the engine. The face 5 of the piston is slightly convex, so that the fresh charge entering the cylinder in the scavenging process circles around the surface of the piston. which is effectively cooled thereby. The lower face of the reentrant cylinder head is slightly rounded so as to nest within the upper edge of the thickened part of the slide valve, as shown in Fig. 2; this forms a small combustion chamber bounded by the reentrant cylinder head, the thickened part 25 of the slide valve and the face 5 of the piston, with the spark plug I located centrally, resulting in efficient combustion. As was already stated, the temperature of the piston head is not too high because it is cooled by the fresh charge; the same is true of the thickened portion 25 of the slide. Hence the lower and side walls of the small combustion chamber are effectively cooled, whilst the lower face of the reentrant cylinder head is cooled directly by cooling liquid surrounding the tube 8. Moreover, the piston and slide valve are preferably made of a metal of good heat conductive properties, such as aluminum or an aluminum alloy. All these features, as well as the eflicient manner in which the combustion gases are scavenged from the cylinder tend to check detonation.

On account of their relatively small number, the gas currents entering the cylinder in the initial stage of scavenging are powerful and are so directed that, without impinging on each other, they practically fill the whole section of the slide valve in a horizontal plane. Also, considering a vertical section, impinging is practically avoided because the gas jets are directed upwardly. In following the courses of the individual jets of the fresh charge it is found that they can ascend as it were spirally side by side. This causes the combustion gases present in the cylinder to be displaced very effectively, which likewise counteracts the tendency to detonate.

It was found that by the various combined features the maximum compression ratio of a fuel with an octane number of 70, which ratio amounted to approximately 1:4.5 for other engines of corresponding cylinder capacity, could be raised to approximately 1:? in the case of the engine according to the invention without giving rise to detonation.

I claim as my invention:

1. A two-stroke cycle internal combustion engine having a cylinder; a reentrant cylinder head spaced from the cylinder wall to provide an annular recess; axially displaced inlet and exhaust ports in said cylinder wall; a piston in said cylinder having a slightly convex upper face which rises from the margin thereof to a radially inner crown by a height which is less than the radius of the piston face; a slide valve extending above said piston face and carried by said piston disposed to control said exhaust port, shaped to enter said annular recess, and having a thickened portion near the upper face of the piston to reduce the internal diameter of the slide; and a plurality of inlet ducts in said slide valve extending through said thickened portion located for registry with said inlet ports and having the projections of their center lines onto a plane perpendicular to the center line of the cylinder tangent to a circle smaller than the internal diameter of the thickened portion of the slide valve and drawn about said center line of the cylinder, and having their inner ends-inclined upwardly.

2. The engine according to claim 1 wherein the slide valve has from 2 to '7 inlet ducts the lower walls of which merge smoothly with the face of the piston, said face being smooth and continuously convex over said crown.

3. The engine according to claim 1 wherein the lower face of the reentrant cylinder head is slightly convex toward the piston, and is shaped to nest within the upper edge of the thickened portion of the slide valve, the height and shape of the top of the thickened portion being such as to rise above the lowest part of the cylinder head and to move into close nesting relation to the lower face of the cylinder head to cover a part thereof when at top dead center, whereby the diameter of the combustion chamber is reduced when the piston is at top dead center, and a spark plug is mounted centrally on said cylinder head.

4. The engine according to claim 3 wherein the slide valve has from 2 to '7 inlet ducts; and the ducts have an aggregate width, measured peripherally, equal to between about 0.4 and 0.6 of the inside circumference of the slide valve above said thickened portion and are disposed to discharge the fresh charge toward the upper edge of the said thickened portion; and the face of the piston is smooth and continuously convex over said crown to permit the fresh charge entering through said ducts to circle around the surface of the piston and to spiral upwardly.

5. The engine according to claim 1 wherein a part of said slide valve has a wearing surface with respect to a non-reciprocating part of the engine, the slide valve is made of a metal of the class consisting of aluminum and aluminum alloys and the wearing surfaces of the slide valve are coated with a layer of hard metal.

6. The engine according to claim 1 wherein the face of the piston is smooth and continuously convex over said crown and the said projections of the center lines of the inlet ducts are tangent to a circle having a radius between about 0.1 and 0.3 of the internal radius of the slide valve above said thickened portion.

7. The engine according toclaim 1 wherein the thickened height and shape of the top of the portion is such as to come into close proximity to the lower face of the cylinder head to cover a part thereof when at top dead center and the radial thickness thereof is such that the internal diameter of the slide valve at the piston face is reduced to between about 0.75 and 0.85 of the internal diameter of the slide above said thickened portion.

8. A two-stroke cycle internal combustion engine having a cylinder; a reentrant cylinder head spaced from the cylinder wall to provide an annular recess; axially displaced inlet and exhaust ports in said cylinder wall; a piston made of a metal of the class consisting of aluminum and aluminum alloys Within .said cylinder having integral therewith a slide valve extending above the piston head, said slide valve controlling said exhaust and inlet ports and being shaped to enter said annular recess; one or more stationary packing rings on the outer wall of said reentrant cylinder head cooperating with the inner face of said slide valve; and a layer of hard metal on at least the portion of the slide valve on contact with said packing rings.

9. The engine according to claim 8 wherein the hard metal is chromium.

10. A two-stroke cycle internal combustion engine having a cylinder; a reentrant cylinder head spaced from the cylinder wall to provide an annular recess, the lower face of said head being slightly convex; axially displaced inlet and exhaust ports distributed circumferentially in said cylinder wall; a piston in said cylinder having a slightly convex and continuously upper face which rises gradually from all ports of the margin thereof to a central crown having a height above said margin substantially less than the radius of the piston face; a slide valve extending above said piston face and carried by said piston disposed for controlling said exhaust port shaped to enter said annular recess, and having a portion near the upper face of the piston so thickened as to reduce the internal diameter of the slide valve at the piston face to between about 0.75 and 0.85 of the internal diameter of the slide above the said thickened portion and extending to a height to come into close proximity with the lower face of said head so as to cover a part thereof when the piston is at top dead center; a plurality not exceeding six inlet ducts in said slide valve extending through said thickened portion located for registry with said inlet ports and having the projections of their center lines onto a plane perpendicular to the center line of the cylinder tangent to a circle drawn about said center line of the cylinder, with radius between about 0.1 and 0.3 of the internal radius of the slide valve above said thickened portion, said ducts having their inner ends inclined upwardly toward the upper edge of said thickened portion, and having an aggregate width, measured peripherally, equal to between about 0.4 and 0.6 of the inside circumference of the slide valve above said thickened portion.

11. The engine according to claim 10 wherein the lower face of the reentrant cylinder head is rounded convexly at the margin and above said lower face thereof and the upper edge of the thickened portion of the slide is rounded concavely to permit the former to nest in the latter. the said concavely rounded part on the slide being at a height to surround the lower part of the cylinder head substantially without clearance when the piston is at top dead center.

12. The engine according to claim 10 wherein the slide valve has a length to cover said exhaust ports throughout the operation and is provided with a plurality of outlet ducts located for registry with said exhaust ports and having their inner edges rounded.

JOHANN'ES T. M. SCHLAMANN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,006,887 Church July 8, 1913 1,124,721 Galbreath et al7 Jan. 12, 1915 1,151,434 Appleton Aug. 24, 1915 1,306,661 Dolne-Dehan June 10, 1919 1,854,285 Williams Apr. 19, 1932 2,337,668 Larson Dec. 28, 1943 FOREIGN PATENTS Number Country Date 593,241 France of 1925 

